1. Field of the Invention
The present invention relates to a semiconductor device which includes a circuit including a semiconductor element such as a transistor, and a manufacturing method of the semiconductor device. For example, the present invention relates to a power device which is mounted on a power supply circuit; a semiconductor integrated circuit including a memory, a thyristor, a converter, an image sensor, or the like; and an electronic device on which an electro-optical device typified by a liquid crystal display panel, a light-emitting display device including a light-emitting element, or the like is mounted as a component.
In this specification, a semiconductor device generally refers to a device which can function by utilizing semiconductor characteristics; an electro-optical device, a light-emitting display device, a semiconductor circuit, and an electronic device are all included in the category of the semiconductor device.
2. Description of the Related Art
Many transistors formed over a glass substrate or the like are manufactured using amorphous silicon, polycrystalline silicon, or the like, as typically seen in liquid crystal display devices. Although a transistor manufactured using amorphous silicon has low field-effect mobility, it can be formed over a larger glass substrate. On the other hand, although a transistor manufactured using polycrystalline silicon has high field-effect mobility, it is not suitable for being formed over a larger glass substrate.
Other than a transistor manufactured using silicon, a technique in which a transistor is manufactured using an oxide semiconductor and applied to an electronic device or an optical device has attracted attention in recent years. For example, Patent Document 1 and Patent Document 2 disclose a technique by which a transistor is manufactured using zinc oxide or In—Ga—Zn-based oxide as an oxide semiconductor and is used as a switching element of a pixel of a display device or the like.